D SP

0 0.5 1 1.5 20

1F

requ

ency

res

pons

e

f/fs

Analog filter

f 0

The frequency response of the digital counterpart of this analog filter is periodic. Therefore in the case of DSP filtering the frequencies in the analog input signal have to be restricted by analog filters so that they do not appear outside the shaded area.

D SP

0 0.5 1 1.5 20

1F

requ

ency

res

pons

e

f/fs

Analog filter

f 0

00

1

Fre

quen

cy r

espo

nse

0.5 1 1.5 2f/fs

Digital filter - uniform sampling

f0

D SP

0 0.5 1 1.5 20

1F

requ

ency

res

pons

e

f/fs

Analog filter

f 0

DASP filters of this type are unique as their frequency responses might be close to the responses of respective analog filter shown above. Therefore they are applicable for extraction of any frequency even if it exceeds the signal sampling rate many times.

D SP

0 0.5 1 1.5 20

1F

requ

ency

res

pons

e

f/fs

Analog filter

f 0

0 0.5 1 1.5 20

1

Fre

quen

cy r

espo

nse

f/fs

Small samplinginterval variance

Digital filter - nonuniform sampling

f0

D SP

0 0.5 1 1.5 20

1F

requ

ency

res

pons

e

f/fs

Analog filter

f 0

While the DASP filter characteristic is good for the passband frequencies, not so well suppressed peaks may appear in the stopband area. More pronounced sampling irregularities help to suppress them.

D SP

0 0.5 1 1.5 20

1F

requ

ency

res

pons

e

f/fs

Analog filter

f 0

f00 0.5 1 1.5 20

1

Fre

quen

cy r

espo

nse

f/fs

Large sampling interval variance